Method of casting copper anodes using a preheated mold coating

ABSTRACT

In the coating of interior surfaces of copper molds with a slurry of a release material prior to the casting thereinto of molten impure copper for the production of anodes for use in the electrolytic refining of such impure copper, the improvement wherein the slurry is heated to a temperature of from about 150* to about 200*F. prior to its being applied, resulting in greatly increasing the operating life of the molds.

United States Patent [191 Cruz et a1.

[451 Feb. 25, 1975 METHOD OF CASTING COPPER ANODES USING A PREHEATEDMOLD COATING [75] Inventors: Ramon C. Cruz, Hayden; Clyde L.

Light, Winkleman; Donald .1. Nelson, Kearny, all of Ariz.

[73] Assignee: Kennecott Copper Corporation,

New York, N.(.

[22] 7 Filed: Jan. 4, 1974 [21] Appl. No.; 430,740

[52] us. Cl. 164/72, 117/523 51 Int. Cl. 1322c 3/00 [58] Field of Search164/72, 130; 117/53 [56] References Cited UNITED STATES PATENTS1,662,354 3/1928 'williams 164/72 3/1964 Pichler 164/72 X 6/1970Zimmerman; 164/72 X Primary Examiner-Francis S. Husar AssistantExaminer-John E. Roethel Attorney, Agent, or Firm-Mallinckrodt &Mallinckrodt [57] ABSTRACT 4 Claims, N0 Drawings METHOD OF CASTINGCOPPER ANODES USING A PREHEATED MOLD COATING BACKGROUND OF THEINVENTION 1. Field The invention relates to the production of copperanodes for use in the electrolytic refining of impure copare cast insolid copper molds weighing up to 6,000 or more pounds. It is commonpractice to treat the interior surfaces of such a mold before each pourwith a slurry made up ofa finely divided inorganic release material,such as silica, suspended in a liquid medium, such as water. The liquidmedium is vaporized by the heat of the mold, resulting in the depositionof a coating of the release material on the interior surfaces of themold. The temperature of the mold during the treatment with the slurryis normally between about 200 and 1,000F. Molten copper, at atemperature of 2,000F. or more is introduced into the treated mold andthe mold is then cooled until the molten metal has solidified. The castcopper anode is removed, and the mold is again treated with the slurryfor the subsequent pour. Cracking of the molds is a serious problem thathas long plagued the casting operation. Small cracks develop in a moldafter about a week of use, and the small cracks rapidly enlarge to anextent that makes it necessary to take the mold out of service andreplace it with a new mold. The cracking problem has long beenconsidered to be a difficulty that simply had to be tolerated, and moldshave customarily been replaced after only short intervals of use.

SUMMARY OF THE INVENTION In accordance with the present invention, theslurry that is normally applied at room temperature or below to theinterior surfaces of a copper anode mold is heated, before application,to a temperature of from about 150 to about 200F. and is applied to themold within that temperature range.

The release agent may be selected from the group consisting of silica,bone ash, alumina, clay, ganister, lime, and graphite, and is slurriedwith a liquid medium capable of being volatilized at the temperature ofthe mold, i.e., from about 200 to 1,000F. In accordance withconventional practice, the release agent is finely divided silica andthe liquid medium is water. The heated slurry is applied to the interiorsurfaces of the mold by conventional means, usually by spraying, butother methods of applying it may be used, e.g., painting, splashing, orotherwise allowing the slurry to flow over the surfaces of the mold toform a coating thereon.

, The residual heat remaining in the mold from pour to DETAILEDDESCRIPTION OF THE BEST MODE CONTEM PLATED Conventional castingprocedures are preferably followed in carrying out the invention. Thus,the usual casting which is normally employed, with the molten copperbeing poured sequentially from the usual ladle into a series of solidcopper molds carried circumferen tially of the wheel. The onlydifference over conventional practice is the heating of the usual slurryprior to its application to the interior surfaces of the molds.

Heating of the slurry may be accomplished in any suitable manner, but isconveniently carried out by injecting steam into the reservoir of slurrymaintained at the usual mold-coating station.

The sequence of steps involved in conventional casting operationscomprises pouring molten copper into the mold, cooling the mold,removing the solidified copper casting from the mold, and applying acoating of the slurry to the interior surfaces of the empty molds. Theempty molds are then returned to the pour step and the sequence isrepeated. The slurry comprises a finely divided release materialsuspended in a liquid medium. The residual heat remaining in the moldfrom pour to pour vaporizes the liquid medium from the slurry coating,leaving a coating of the release material on the interior surfaces ofthe mold. The molds can be cycled through the sequence of steps as agroup, or, preferably, they are cycled therethrough sequentially in acontinuous series.

The inorganic release material contained in the slurry includes suchmaterials as silica, bone ash, alumina, clay, ganister, lime andgraphite, preferably silica. The liquid medium is preferably water. Theslurry itself may vary in the concentration of solids present dependingupon the method of applying the slurry to the surfaces of the molds. Forspraying operations, the solids concentration may be as low as 2 percentto 5 percent by weight, but generally will be between about 10 percentand 25 percent by weight. In splashing and other methods of applyingtheslurry to the mold surfaces, the solids concentration may be as highas percent by weight. The particle size of the solids in the slurry canalso vary over a wide range depending upon the method of applying theslurry to the surfaces of the molds. For spraying operations, theparticle size is preferably such that the dry solids are capable ofpassing through a 200 mesh screen. For other methods of applying theslurry to the mold surfaces, the particle size of the solids is notcritical, the only requirements being that a homogeneous slurry bemaintained, and that the coating of solids applied to the mold surfacesis uniform. Generally, the solids will have a particle size capable ofpassing through a 200 mesh screen.

The temperature of the mold during the application of the slurry theretois generally between about- 200and 1,000F. The residualheat remaining inthe molds from pour to pour, as mentioned hereinbefore, vaporizes theliquid medium from the slurry coating, leaving a residual coating of therelease material on the interiorsurfaces of the mold.

Cooling of the mold following a pour can be accomplished by circulatingwater through internal passage- EXAMPLE A comparison test was run usingthe apparatus of a conventional, operating facility for producing castcopper anodes. The apparatus comprised a casting wheel which supported aseries of copper molds, each were weighing approximately 6,000 pounds.Each mold was capable of casting a 700 pound copper anode. As thecasting wheel rotated, each of the molds supported thereon progressivelyadvanced from a filling station wherein molten copper was charged to themolds, to an anode discharge station where the anodes, which had cooledand solidified during their travel between the filling station and thedischarge station, where removed from the molds. The empty molds thenmoved past a mold wash station wherein a slurry of silica in water wasapplied as a coating to the interior surfaces of the mold. Thetemperature of the molds during the application of the silica slurrygenerally was between about 300F. and 1,000F., and the heat content ofthe molds rapidly vaporized the water content of the slurry coating,leaving only a coating of silica on the surfaces of the mold. The moldswere then returned to the filling station.

This casting cycle had been operated commercially for several yearsusing a slurry comprising approximately 500 pounds of silica to 500gallons of water. The silica used had a particle size capable of passingthrough a 200 mesh screen. The temperature of the silica solution as itwas applied to the molds was approximately that of the ambientatmosphere, i.e., between about 50and about 100F. Experience with thisprocess indicated that small cracks developed in the molds after aboutone week of use, and the small cracks would rapidly increase in size towhere the mold had to be discarded.

In the comparison test, all of the molds on the casting wheel, with theexception of one, were replaced with new molds. One old mold, which haddeveloped one small crack, was left in place on the casting wheel. Theprocedure used in casting anodes with the new molds was exactly as givenhereinabove with the single exception that the silica slurry was heatedto a temperature about 150and 200F. prior to its being applied to thesurface of the empty molds. Following a two months period in which thesemolds were continuously used in casting copper anodes, not a singlecrack developed in any of the new molds which had been installed on thecasting wheel. The one old mold, which has a small crack therein at thestart of the two months test, still had only one crack therein, and thatone crack was of the same size that it had been at the beginning of thetwo months test.

Whereas, there is here described a certain preferred procedure which ispresently regarded as the best mode of carrying out the invention, itshould be understood that various changes may be made and otherprocedures adopted without departing from the disclosed inventiveconcepts particularly pointed out and claimed hereinafter.

What we claim is:

1. In the casting of copper anodes wherein copper molds are successfullyfilled with molten copper and the solidified anodes are successivelyremoved therefrom on a cyclic basis, and coatings of a release materialare applied as a slurry thereof in a liquid medium to the internalsurfaces of the respective molds prior to the introduction of the moltencopper thereinto, the improvement wherein the slurry is heated andapplied to the interior surfaces of said molds at a temperature of fromabout 150 to about 200F.

2. A method in accordance with claim 1, wherein the liquid medium iswater.

3. A method in accordance with claim 2, wherein the release agent issilica, and the temperature of the mold during the application of therelease agent thereto is within the range of about 200 to about 1,000F.

1. IN THE CASTING OF COPPER ANODES WHEREIN COPPER MOLDS ARE SUCCESSFULLYFILLED WITH MOLTEN COPPER AND THE SOLIDIFIED ANODES ARE SUCCESSIVELYREMOVED THEREFROM ON A CYCLIC BASIS, AND COATINGS OF A RELEASE MATERIALARE APPLIED AS A SLURRY THEREOF IN A LIQUID MEDIUM TO THE INTERNALSURFACES OF THE RESPECTIVE MOLDS PRIOR TO THE INTRODUCTION OF THE MOLTENCOPPER THEREINTO, THE IMPROVEMENT WHEREIN THE SLURRY IS HEATED ANDAPPLIED TO THE INTERIOR SURFACES OF SAID MOLDS AT A TEMPERATURE OF FROMABOUT 150* TO ABOUT 200*F.
 2. A method in accordance with claim 1,wherein the liquid medium is water.
 3. A method in accordance with claim2, wherein the release agent is silica, and the temperature of the moldduring the application of the release agent thereto is within the rangeof about 200* to about 1,000*F.
 4. A method in accordance with claim 1,wherein the release agent is a member selected from the group consistingof silica, bone ash, alumina, clay, ganister, lime, and graphite.